A coke plant which manufacturers coke from coal for subsequent use in blast furnaces or foundries for making iron therefrom employs one or more coke oven batteries. A coke oven battery is a bank of coke ovens positioned side by side. A coke oven battery can contain a fairly substantial number of coke ovens, spanning a length of several hundred feet.
One side of the coke oven battery is known as the "pusher" side, while the opposite side of the coke oven battery is known as the "door" or "coke" side. On the pusher side, there is a set of railroad type rails or tracks running the length of the battery. Along this set of rails or tracks there rides what is known as a "pusher side machine" or simply "pusher machine". This pusher machine can weigh on the order of 60 to 220 tons, and carries a variety of equipment which is used in conjunction with the coke oven battery. The pusher machine normally incorporates a number of pieces of functional equipment for use in servicing the ovens, including a door extractor for removing and reattaching an oven door to its oven, a door cleaner for cleaning foreign material from the oven door, an oven jamb cleaner for cleaning foreign material from the oven jamb, a pusher ram for pushing the coke through the oven and out the opposite door, and a leveler for insertion through a separate leveler door at the upper end of the coke oven door for levelling the coal loaded from above into the oven.
The opposite side of the coke oven battery, known as the "coke side", similarly includes a set of rails or tracks, with a somewhat smaller "coke side machine" or simply "coke machine" or "door machine" that rolls therealong. The door machine similarly includes a door extractor, a door cleaner and a jamb cleaner, but includes no pusher ram or leveler. The door machine includes a coke guide which is a rectangularly cross-sectioned chute used for directing the coke from the coke oven over and across the set of rails or tracks and into one or more conventional railway cargo cars known as "hot cars".
In order to utilize the various pieces of equipment on either the pusher machine or door machine in conjunction with a selected oven, the piece of equipment carried by the machine must be aligned with the vertical centerline axis of symmetry of the selected oven which is to be serviced. Positioning the equipment carried by the machine so that its vertical centerline axis of symmetry is aligned with that of the selected oven is known as placing the machine or equipment "on spot".
Some coke plants still use the visual method whereby the operator looks across a sight in the cab to line up on a mark on a buckstay or other structure. Others use a hydraulic cylinder mounted on the door or pusher machine with a receptacle mounted on buckstays or other structures and the operator extends the cylinder shaft into the receptacle having a limit switch to signal success. Some coke plants have tried laser spotting systems but not very successfully. The laser fires a beam to a mark on a buckstay.
Another type of completely manual system for placing the functional equipment of the machine "on spot" has been developed and marketed by the assignee of the present invention. In that spotting system, the pusher or door machine has installed on the top thereof a sprocket driven 500 count encoder/pulse generator having a high speed count/pulse module. An encoder chain is mounted from the face of the battery, e.g. the hot rail outriggers to span the length of the coke oven battery, and is positioned to mesh with the sprocket driven encoder as the machine travels along the tracks. This system further includes a programmable logic controller having a minimum of 6K of memory, 16 bits of discrete inputs, 16 bits of discrete outputs, a chassis, a power supply for the chassis, a Panelview display for operator input and display output, and a limit switch for resetting the encoder at the zero location all purchased from Allen Bradley. As the machine travels down the tracks, the encoder sprocket is driven by the encoder chain. The computer is programmed with the position along the chain corresponding to the position of the centerline axis of each oven; therefore for a particular position of the machine along the chain and hence tracks the computer knows the distance between the machine, and hence the functional equipment carried by the machine, and the centerline of any selected oven. Consequently, via the Panelview display, the computer will indicate to an operator the direction the machine must travel in order to align the selected piece of equipment carried by the machine with the selected oven. The operator energizes the travel controller by pushing the appropriate button on the Panelview display to move the machine in one direction along the rails, or reverses the travel controller to move the machine in the other direction along the rails. The Panelview display continues to indicate the direction in which the car is required to be moved to align the piece of equipment with the selected oven. When the machine gets near the selected oven the operator slows the machine, and then gradually moves the machine on spot using the manually operated travel controller. Should the operator cause the machine to overshoot the on spot position, the Panelview display simply indicates that the machine must then be moved in the opposite direction. The operator so jockeys the machine with the manual travel controller until the Panelview display indicates on spot.
The resolution of the sprocket driven encoder in combination with the chain is on the order of plus or minus 0.025 inch. However, due to the limitations of a human operator's manual dexterity in operating the travel controller, an operator is normally only able to position or spot the machine and its associated equipment within plus or minus 1/2" of the true on spot position. Consequently, via this manual type of spotting, an operator is unable to exploit the resolution of the encoder as he is normally off of true on spot by plus or minus 1/2". By being off by as much as plus or minus 1/2", the equipment carried by the pusher machine and door machine can be damaged, and can damage the coke oven door and the door jamb. For example, when replacing a door that has been extracted from its oven, a variation of plus or minus 1/2" from true on spot can greatly damage the seal of the coke oven door and/or the jamb of the coke oven itself. This damage results in downtime of the oven and costly repair is required to repair the door jamb and/or door seal. Similarly, if the jamb cleaner is off by as much as plus or minus 1/2", it likewise can become damaged and/or damage the door jamb. The same is true if the pusher ram is off by as much as plus or minus 1/2".